Non-invasive method and apparatus to detect and monitor early medical shock, and related conditions

ABSTRACT

A diagnostic medical instrument adapted to determine whether a patient is suffering from a pre-shock, shock, or shock-related condition. The instrument is used in a capillary filling time CFT test procedure in which a skin area in the patient which overlies blood-filled capillaries which normally display a pink color is depressed to expel blood from the capillaries and impart white color to the skin at which point the pressure is released to permit blood to flow back into the capillaries and cause the skin to regain its pink color. The instrument includes a color sensor trained on the sign area and responsive to light reflected therefrom to produce a first signal at the point in time the skin color turns from pink to white and to later produce a second signal at the point in time at which the skin color has turned from white to pink. The time elapsing between the first and second signals is measured to provide a CFT index indicative of the patient&#39;s condition.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of prior PCTapplication no. PCT/IL00/00443, file Jul. 25, 2000, designating theUnited States and in which Demand was filed on Feb. 19, 2001, electingthe United States, published in English under PCT Article 21(2) and nowabandoned.

FIELD OF THE INVENTION

This invention relates generally to the diagnosis of medicalshock-related conditions and to instruments for this purpose. Moreparticularly, the invention relates to methods and apparatus for thenon-invasive detection of pre-shock, shock and shock-related conditions(other related causes of cardio-pulmonary distress), and for assistingin a patient's recovery from these conditions by monitoring changes incapillary flow in skin areas of peripheral body organs.

BACKGROUND OF THE INVENTION

The normal skin color at most sites on the human body is generally pink.Skin color depends on the amount of blood flowing in the capillariesthrough which blood flows from the arterioles to the venules. Thepresent invention resides in non-invasive detection of hemodynamicchanges in the skin arteriolar-capillary flow during states ofpre-shock, shock and cardio-pulmonary distress. These changes areindicative of a reduction in blood delivery to an organ of the body.

Expressed in its simplest terms, shock is the consequence of aninadequate delivery of blood to a major organ of the human body. Unlessshock is promptly treated, this deprivation of blood may give rise to adisturbance in the metabolism of the organ with a resultant damagethereto. Because of the serious consequences of shock, its detection andtreatment is regarded medically as an emergency procedure in which timeis of the essence.

Cellular damage to an organ may be reversed by prompt treatment ofshock. But it is otherwise irreversible and may lead to the death of thepatient. Recovery from shock therefore depends on the promptness oftreatment. However, before a patient can be treated for shock he mustfirst be diagnosed to determine whether the patient is actuallyexperiencing shock.

The treatment to be administered to a patient in shock depends on thenature of his condition. For example, for some shock conditions theappropriate treatment includes fluid resuscitation and the drug dopaminewhich acts to increase arterial perfusion pressure. Treatment for ashock condition must be administered with extreme care while the patientis being monitored.

A significant aspect of diagnostic instrumentation in accordance withthe invention is that it is adapted to monitor as well as to detectshock-related conditions in a non-invasive manner. Using thisinstrumentation, one can make, even in a pre-hospital setting, an earlydiagnosis of shock as well as determine whether the drug beingadministered to a patient in shock is having the desired therapeuticeffect.

Medical authorities classify shock syndrome in the follow fivecategories:

(1) Hypovolemic shock

(2) Septic shock

(3) Cardiogenic shock

(4) Obstruction to cardiac filling shock

(5) Neurogenic shock

Hypovolemic shock, the most common type of shock, is caused by a massiveloss of blood, plasma or fluid from the body of a patient, or the lossof fluid from an intravascular compartment. Such losses may be due todehydration, vomiting, diarrhea, burns, or because of the abusive use ofdiuretics. A loss of blood and plasma is experienced in hemorrhagicshock such as in cases of blunt and penetrating trauma injuries,gastrointestinal bleeding, or Gynecologic/Obstetric bleeding. Many casesof bleeding are occult (e.g. slow internal bleeding), and therefore cannot be diagnosed early.

Septic shock is caused by bacterial infection in which an endotoxin isreleased into the blood stream. The sequestration and pooling of bloodin various vascular compartments reduces the availability of blood forthe perfusion of other vital organs.

Cardiogenic shock is usually attributed to a massive myocardialinfarction caused by extensive damage to the myocardium. This may be theresult of arrhythmia in a patient suffering from heart disease. In thiscategory of shock syndrome, the heart fails to pump properly, with aconsequent reduction in arterial blood.

Obstruction to cardiac filling shock takes place when this fillingactivity is lessened or arrested by a massive pulmonary embolism, or byspace-occupying lesions. Neurogenic shock results from a severe spinalcord injury, or from a massive intake of a depressant drug, causing aloss of vasometric tone.

The five categories of shock syndrome each represent other causes ofcardio-pulmonary distress, or a shock-related condition. The term“shock-related condition”, as used hereinafter, is ended to embrace allfive categories.

The onset of a shock condition is characterized by the reduction inblood flow to skin tissue (decreased skin perfusion). This reduction inskin perfusion is the result of a profound vasoconstriction of the skintissue arterioles, which leads to decreased capillary flow, and aresultant poor perfusion to the skin. In order to diagnose an earlystage of shock, one must detect this early reduction in skin capillaryflow. A useful clinical, bed-side test for poor skin perfusion is anestimation of Capillary Filling Time (CFT). When applying pressure ontoa specific skin area, the capillaries below the depressed area collapseand blood is blanched therefrom, hereby causing the skin color in thedepressed skin area to whiten. Upon abrupt release of this pressure,blood flows back into the capillaries and the original skin color isrecovered.

CFT is defined as the time it takes for the original pink skin color toreturn after it had been blanched. In clinical practice, prolongation ofthe CFT for more than 2 second is considered a state of shock resultingfrom poor skin perfusion. This well-known bed-side test, althoughsubjective and inaccurate, is an important vital sign of a shock state.If an appropriate treatment has not been given early enough, the shockcondition will continue to deteriorate, the arteriolar vasoconstrictionwill increase even further, as reflected by prolongation of the CFT,blood pressure will fall, and the patient may die. However, anappropriate prompt treatment at the early stage of shock will decreasevasoconstriction and shorten the CFT.

Known non-invasive methods to diagnose shock do not evaluate perfusion.These methods rely on the following cardiovascular parameters:

Blood pressure. An indirect parameter of shock. The measurement of bloodpressure identifies shock only in its late stages when blood pressuredrops (uncompensated shock).

Heart rate. An indirect parameter of shock. The specificity of thismeasurement is low because heart rate is also increased by other commonphysiological conditions, such as anxiety and pain.

The advantage gained by measuring the rate of blood perfusion by way ofCFT instrumentation is that it enables early detection of a shocksyndrome (compensated shock, prior to the reduction of blood pressure)and indicates its severity. This makes possible prompt treatment ofpatients who can then survive a shock-related condition which may befatal if untreated or if treated too late.

Disclosed in U.S. Pat. No. 3,698,382 is an apparatus for measuring venofilling time which applies intermittent and uniform pressure to the skinof a patient. This instrument which measures capillary flow changessecondary to the compression of a vein comprises a light source orilluminating a skin area and photoelectric monitoring means sensitive tothe coloration of the skin area. The instrument measures the rate atwhich color returns to the skin area after pressure thereon is released.However, there are major differences between the '382 apparatus andapparatus in accordance with the invention in that the former measurescapillary flow changes resulting from mechanical pressure applied to anearby vein and these changes in flow do not reflect a state of shock.

When measuring CFT it is essential that pressure be applied only tocapillary vessels while maintaining normal blood flow. In a preferredembodiment of an apparatus in accordance with the invention, aprogrammable mechanical unit applies an accurate measurable amount ofpressure to the skin.

In order to diagnose the condition of shock, one must detect capillaryflow changes resulting from the physiologic stress of shock. Thesechanges in capillary flow are due to vasoconstriction and are notrelated to mechanical pressure applied to a nearby vein. When measuringCFT, it is vital that pressure be applied only to the capillary vesselswhile maintaining normal venous flow. In contradistinction to theapparatus in the '382 patent, an apparatus in accordance with theinvention uses a programmable mechanical unit that applies accuratemeasurable pressure to the skin, which increases gradually, until apoint of maximal skin whitening has been detected. This technique makesit possible to find the MINIMAL blanching pressure which results inmaximal whitening. At minimal blanching pressure, blood is moved awayfrom the capillaries while maintaining normal flow in the veins. Thistechnique is the hallmark of measuring true systemic changes incapillary flow.

The '382 patent apparatus is subject to interference from external lightsources and therefore requires an opaque housing for the monitoringapparatus. The apparatus does not measure skin temperature which has anindependent effect on capillary flow. In addition, the mechanicalarrangement required for maintaining uniform pressure in order to attainmore accurate readings is cumbersome and costly.

They are also relatively complex and expensive and difficult tointerpret clinically (laser Doppler devices for example). Time is of theessence in the diagnosis and treatment of shock, yet known types of skincapillary flow instrumentation are incapable of facilitating rapiddiagnosis and treatment of shock. It is vital that skin capillary flowinstruments have a high order of accuracy so that their readingsindicate the severity of the shock or shock-related condition.

Studies published in the medical literature over the last two yearsdemonstrate that ski temperature independently influences the skincapillary flow. One major limitation of prior skin capillary flowmeasurement devices is that they do not take into account skintemperature, and therefore do not correlate the measurement to skintemperature. This correlation enables real-time analysis of the state ofshock. In contradistinction, a device in accordance with the inventionmeasures skin temperature prior to each CFT measurement so that everyCFT measurement is correlated to the change in skin temperature.

Of general background interest is U.S. Pat. No. 4,494,550 whichdiscloses apparatus for the non-invasive detection of venous andarterial blood flow drainage disorders which is designed for thedetection of flow abnormalities in the large vessels of a limb. Also ofbackground interest is U.S. Pat. No. 5,050,613 (1991) which discloses avascular testing apparatus. This includes capillary blood flow sensorsto measure the blood flow of a patient. This diagnostic tool acts todetermine the overall vascular integrity of a patent, but is unable anddoes not diagnose shock or shock-related conditions

SUMMARY OF THE INVENTION

In view of the foregoing, the main object of this invention is toprovide a diagnostic method and an instrument for carrying out themethod to determine accurately whether a patient is suffering from astate of shock and shock-related conditions, as well as to measure andmonitor the severity of this physiologic condition.

In particular, an object of this invention is to provide a non-invasivemethod and apparatus adapted to detect pre-shock, shock andshock-related conditions by ongoing measurements of the patient'scapillary filling time (CFT).

A significant advantage of an apparatus in accordance with the inventionis that it can expedite recovery by monitoring changes in capillary flowin skin areas of peripheral body organs. The CFT measuring instrumentprovides a rapid yet accurate reading of the patient's condition, makingit possible to treat the patient without delay to avoid damagingconsequences.

It is also an object of this invention to provide a CFT diagnosticinstrument which is of relatively simple design and easy to operate.

Briefly stated, these objects are attained in a diagnostic medicalinstrument adapted to determine whether a patient is suffering from apre-shock, shock, or shock-related condition. Some shock-relatedconditions are related to inadequate flow in a specific organ. Thesemedical conditions are common in patients after orthopedic surgery, flapreconstruction surgery, or patients who suffer from a severe peripheralvascular disease. By being highly sensitive to changes in capillaryflow, an apparatus in accordance with the invention is applicable tothese medical shock-related conditions.

The instrument is used in a capillary filling time test procedure inwhich a skin area in the patient overlying blood-filled capillarieswhich normally display a pink color, is depressed to expel blood fromthe capillaries and to blanch the skin and impart a white color thereto.When a point of blanching has been attained at a minimal pressure point,the pressure is then released to permit blood to flow back into thecapillaries and cause the skin to regain its natural pink color. Usingthis minimal blanching pressure technique, blood is withdrawn from thecapillaries whereas venous blood flow remains almost intact.

The instrument includes a color sensor trained on the skin area andresponsive to light reflected therefrom to produce a first signal at thepoint in time the depressed skin color is blanched from pink to whiteand pressure is released when blanching at minimal pressure is attained,to later produce a second signal at the point in time at which the skincolor regains its natural pink color. When the post-blanching skin colorcorresponds to a pre-test natural color, the CFT can be detected byrecording the time which has elapsed from the maximal blanching point tothis final point. In other words, the time elapsing between the firstsignal (starting point of minimal blanching pressure release) and thesecond signal (final point where post-blanching color equals pre-testcolor) is measured to provide a CFT index indicative of the patient'scondition at the time the test was conducted.

For each pre-determined time interval, this measurement is repeated anda new CFT is recorded.

The device will continue measuring CFT every 30 seconds to 1-5 minutes(this depends on clinical demands), and a change of CFT over time willbe recorded and monitored. This change in CFT, or d[CFT]/d[t], reflectsskin perfusion changes over time and measures deterioration orimprovement of shock state.

In one preferred embodiment of the invention, the color sensor includesa video camera trained on the skin area of the patient and responsive tolight reflected from this area to yield an image signal whose characterdepends on the existing color of the skin.

In another embodiment, the skin area is illuminated by a beam of lightmodulated at a predetermined frequency, the pulsed light reflected fromthis area being intercepted by a photosensor whose output signal isindicative of the skin color.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention as well as other objects andfeatures thereof, reference is made to the annexed drawings wherein;

FIG. 1A illustrates the structure of a skin color sensing apparatus forthe diagnosis of a shock-related condition in a patient by measuring thecapillary filling time and rate in accordance with a first embodiment ofthe invention;

FIG. 1B schematically illustrates the color sensor included in theapparatus shown in FIG. 1;

FIG. 2 is a block diagram of the apparatus shown in FIG. 1 for thediagnosis of a shock-related condition in a patient by measuringcapillary filling time aid rate;

FIG. 3A is a graphical representation of the measurement CFT results;

FIG. 3B is a graphical representation of CFT, as a function of the levelof shock, for obtaining inferences related to the trend of the patient'sphysiological condition in reaction to medical treatment;

FIG. 4 schematically illustrates how the apparatus is used, as shown inFIG. 2, for the diagnosis of pre-shock state in a patient;

FIG. 5 illustrates the color sensor included in a second embodiment of aCFT diagnostic instrument;

FIG. 6 is a block diagram of the apparatus included in the secondembodiment;

FIG. 7 is a graph showing the relationship between CFT readings andconditions of shock;

FIG. 8 is a graph showing the relationship of skin temperature on CFTreadings.

DETAILED DESCRIPTION OF THE INVENTION

First Embodiment: Schematically illustrated in FIG. 1A is a CFTinstrument 450 adapted to diagnose a shock-related condition in apatient by measuring capillary filling time and rate.

Instrument 450 includes a camera 412, such as a color video camera,fixed in place by a holder 414 above a rigid table surface 411 on whichan appendage 410 of a patient rests. This appendage may for example bethe patient's finger. The position of camera 412 is adjusted so that theskin area 413 viewed by the camera for purposes of CFT measurement, isin or is close to the focal plane of the lens. Pressure may be appliedto and released from skin area 413 manually or by using mechanicalapparatus which may be automatically controlled.

Skin area 413 is illuminated by background light, and light reflectedfrom the surface of this area is received in the lens of camera 412. Aminimal illumination level of 0.2 lux is sufficient for mostcurrently-available modern cameras for color discrimination. Camera 412generates an electrical signal having a magnitude corresponding to theparticular color of the image received by the camera, this signal beingfed by a line to a processing and display unit 400. In the event theillumination level of the background light is insufficient, skin area413 may be illuminated with a light source, such as a conventional lampor a Light Emitting Diode (LED).

A sensing device 100 as shown in FIG. 1B, is connected to the processingand display unit 400 by an electrical cord through which CFT data is fedfor processing and display. The processing and display unit 400 may be apersonal computer that uses control and processing software to processthe data received by the lens of camera 412, and calculate the CFT totaltime and rate. Pressure is applied and released manually by the user inaccordance with instructions provided by processing and display unit400. The processing and display unit 400 may further include circuitryfor controlling automated application of pressure.

The control circuitry may also be used to select a specific area forprocessing taken from the imaged skin area. Such selection may becarried out, for example, by software which controls the processing. Thesensing device may also be attached to other locations in the patient'sbody that are rich in subcutaneous blood vessels, such as to the lip orto the ear lobe, for measuring the CFT.

FIG. 1B schematically illustrates the structure of a skin color sensingdevice 100 for the diagnosis of a shock-related state in a patient bymeasuring the capillary filling time and rate. Device 100 comprises acamera 412, such as a color video camera, contained in a transparentexternal housing 102, whereby most of the background light entersthrough is external housing and illuminates the skin surface 106.

Device 100 may further include an optional light source 101, such as anLED, operated by a power supply during measurement when backgroundillumination is not at a level sufficient to enable the camera 412 todiscriminate between colors. Eternal housing 102 may be light reflectingwith an opening in its bottom side, so that most of the light radiationemitted from light source 101 is directed toward the bottom side in onedirection “A”.

External housing 102 may also include an opaque internal housing 104,having an opening in its bottom side, so as to enable light radiation toenter into the opaque internal housing space only from its bottom side.Using this structure, camera 412 in internal housing 104 receives mostof the light reflected from the skin. The bottom sides of externalhousing 102 and internal housing 104 are aligned with each other andcovered by a transparent rigid layer 105. Layer 105 acts to applypressure on the skin while enabling light to pass through in bothdirections.

Transparent rigid layer 105 is brought into contact with an exteriorlayer 106 of the skin of the patient being diagnosed. Pressure isapplied manually or automatically on the external housing 102 toward theskin surface in a perpendicular direction A. External housing 102delivers the pressure to the transparent rigid layer 105, whichtransfers it through exterior layer 106 to the interior layer 107 of theskin containing most of the subcutaneous blood vessels (capillaries).When the magnitude of applied pressure is adequate for expelling bloodfrom the capillaries and maintained for a sufficient period of time,blood is forced out of the capillaries and the color of the interiorlayer 107 of the skin becomes much brighter (i.e. close to white).

The background light as well as light radiation emitted from lightsource 101 penetrates the skin and is partially reflected back indirection “B” into internal housing 104. The degree of reflection frominterior layer 107 is inversely related to the blood flow in thecapillaries under pressure inasmuch as blood absorbs light, the moreblood the less the amount of reflected light. The reflected light entersthe lens of camera 412, which produces an electric signal whosemagnitude depends on the instantaneous color of the skin. The positionof camera 412 within the device 100 is arranged so that the exteriorsurface of the transparent rigid layer 105 is essentially in the focalplane of the camera 412. This positioning results in a clear and focusedimage that is received by the camera lens. A focused image sharpens thedistinction between colors and therefore enhances the resolution andaccuracy of the measurement.

Under zero pressure (i.e., full blood flow), a patient's skin color isnormally pink, and less light radiation is reflected back from thecapillaries. When the skin is subjected to a pressure to arrest bloodflow, the skin color then becomes white and more light radiation isreflected back from the capillaries. Therefore, changes in magnitude ofthe electric signal yielded by camera 412 affords an accurate index tocapillary filling time and rate which commences upon releasing thepressure from the skin. Device 100 is connected to a power supply foroperating the optional light source 101 and for operating datacollection, processing and display circuitry for processing the signalsprovided by the camera 412 and displaying the measurement results.

FIG. 2 is a block diagram of an apparatus 200 or the diagnosis of ashock-related state in a patient by measuring capillary filling time andrate in accordance with the invention. Apparatus 200 includes camera412, whose output is supplied to a frame grabber 206 for capturing theimage received by the camera. Light reflected from the skin surface isconverted by camera 412 to a corresponding video signal, such as aComposite Video or a Red-Green-Blue (RGB) Video signal, depending on thetype of camera used, that represents the received image.

The video signal is fed into an electronic circuit (e.g., a FrameGrabber or a Video Capture circuit) which decodes the video signal andconverts it into a corresponding array of digital values, which array isstored in a memory. Each cell of the memory stores a digital value thatrepresents the light intensity and the color of a portion of thereceived image. Camera 412 updates the image at a rate of 50 times persecond, and therefore, the image information, generated by frame grabber206 and stored in the memory array is also updated at the same rate. Arate of 50 times per second usually corresponds to video camerascompatible with Pulse Alteration by Line (PAL) video encoding standards.A rate of 60 times per second usually corresponds to video camerascompatible with National Television System Committee (NTSC) videostandards. Faster video cameras to update the image at higher rates arealso useable.

The digital data is fed into a digital processor 207 which analyzes thedata and display the results on display 208. Processor 207 samples adesired area of the image which contains most of the tested skin area.At the next step, processor 207 calculates the intensity of theessentially pink/red light, reflected by the tested skin area. Theintensity of the rejected light is processed and normalized to abaseline, which may be the normal color of the patient's skin when nopressure is applied. The image information is updated in a ratedetermined by the type of camera included in the system. Processor 207therefore continuously calculates the normalized intensity.

Display 208 presents a display of the calculated results of thenormalized intensity (i.e., the CFT) as well as a graphicalrepresentation of the measurement process as a function of time. Thegraphical representation indicates whether or not the measurementresults are reasonable, and if desired, the measurement can be repeated.Other data processed results, such as statistical data, can be alsodisplayed to provide indications regarding the reaction of the patientto medical treatment.

FIG. 3A is a graphical representation of CFT measurement results. At thefirst stages no pressure is applied on the skin, and therefore theapparatus 200 can carry out calibration of the initial skin color of thepatient. The value of the calibration is stored for use at the end ofthe measurement. The calibration process is essential in that the normalcolor of the skin depends on the individual and differs from patient topatient.

At the second stage of operation, pressure is applied to the skin at amagnitude and for a duration sufficient to obtain maximum whitening ofthe skin color in the depressed area. The processor can be programmed toprovide a warning signal (such as a beep) to the user when the pressureis insufficient or shorter in duration than required. Obtaining maximumwhitening of all the depressed area is indicative of sufficientwhitening pressure.

Stronger pressures, of longer duration do not affect the skin colorbeyond maximum whitening. After obtaining maximum whitening, a signalindicative thereof is provided to the user to quickly release thepressure. Measurement of the CFT is started at that instant (to) atwhich the skin color proceeds to change from its maximum whitening colorto regain its original pinkish color. Normally, the rate of filling ishigher at the beginning of the filling process and lower as time lapses.

The apparatus uses the stored calibration value to determine the momenttf at which the normal pink skin color is regained, at which point themeasurement ceases. The recovery time can be determined by the desireddegree of measurement accuracy. For example, point tf can be defined asthe instant at which the value of the digital word that corresponds tothe current skin color reaches a value that is 90% of the value of thedigital word that corresponds to the original skin color of the patientbeing diagnosed. In the graph of FIG. 3A, the CFT reading is given bytf-to.

The accuracy of the measurement can also be determined by the rate ofchange in the skin coloring in the time interval that is close to theconclusion of the measurement. The last segment of the graph liesbetween the points of time t1 and tf. The rate of change in this timeinterval is nearly constant and is nearly insensitive to the magnitudeand duration of the applied pressure. Hence, the CFT can be extrapolatedwith relatively high accuracy from the time interval tf-t1. Under normalconditions CFT should be below one second. A CFT value above two secondscan be regarded as representing a pre-shock state. Longer CFT values canbe considered to be indicative of more severe shock states.

FIG. 3B is a graphical representation of the CFT as a function ofshock-state for obtaining inferences related to the trend of thepatient's physiological condition in response to medical treatment. Inthe initial time interval between time-points t2 and t3, the CFT valueis then below 2 seconds, hence the patient is in a normal, shock-freecondition. An early and mild shock condition starts at time-points t3where the CFT value exceeds 2 seconds. As time lapses with no propertreatment of the shock condition, the shock becomes more severe untiltime-point t4 is reached. This point indicates the entry of the patientinto a moderate shock condition (CFT value higher than 3 seconds). Thenext stage is indicated by the time-point t5. This indicates the entryof the patient into a late (severe) shock condition (CFT value higherthan 4 seconds). From point t5 and beyond, the CFT rises rapidly.

Analysis of skin temperature is crucial for the clinician to make anappropriate diagnosis and monitoring of shock. For example, very coldskin temperature will independently prolong CFT (an acceptable falsepositive of CFT measurement). For each time interval, the device willmeasure and monitor both CFT and skin temperature. (See “Modified SecondEmbodiment” in connection with FIG. 6).

When a medical treatment is administered to the patient, the CFT ismeasured thereafter on a periodic basis. This measurement is used todetermine whether the pre-shock or the actual shock condition isreversible. If the patient's reaction to the given treatment ispositives then in time the CFT will be reduced, indicating a significantimprovement in the physiological condition of the patient until the CFTvalue goes below the safe 2 Sec level.

FIG. 4 schematically illustrates the use of an apparatus 200 for thediagnosis of pre-shock state in a patient. Apparatus 200 includes a skincolor sensing device 100 attached by straps or by adhesive tape to askin area rich in subcutaneous blood vessels, such as hand fingers, anda processing and display unit 400 coupled to sensing device 100. Device100 is connected to the processing and display unit 400 by an electricalcord through which the CFT data is fed for processing and display.Pressure is applied and released manually by the user in accordance withinstructions provided by processing and display unit 400. The sensingdevice for measuring CFT may also be coupled to other sites in thepatient's body that are rich in subcutaneous blood vessels, such as tothe lip or to the ear lobe.

In practice, an automatic measurement can be carried out by integratinga mechanical control apparatus into sensing device 100 adapted tocontrol the applied pressure and release thereof by an externalcontroller. Such mechanical apparatus may comprise a miniature linearmotor that produces linear movement rather than rotational movement.Alternatively, linear movement pressure can be applied by anelectromagnet or by a rotational motor with an eccentric movementmechanism. The linear movement can be controlled to depress a movablemember, such as a movable transparent rigid layer, against the skin andto release the pressure by a corresponding control command.

Sensing device 100 and the processing and display unit 400 may furtherinclude receiving and transmitting circuits to enable wireless exchangeof data and control commands required for CFT measurements. Wirelessconnection makes feasible a single processing and display unit 400 tocontrol and monitor several sensing devices 100, each attached to adifferent patient. Each sensing devices 100 is identified by a uniquecode assigned to it, to eliminate false associations between processeddata and a patient.

The invention can be carried out in a great variety of other waysemploying techniques which differ from those described herein, such asby using pneumatic apparatus for applying pressure to the patient'sskin, or by using an Infra-Red camera rather than a video camera. Alsoone can store the history of CFT measurements of a patient and displaythe variation of the CFT curve with time.

Second Embodiment: This embodiment of a CFT diagnostic instrumentdiffers from the instrument shown in FIG. 1 mainly in the nature of itsskin color sensor. However, in all other respects it operates in thesame manner as does the first embodiment.

FIG. 5. Schematically illustrates the structure of a skin color sensingdevice 500 for the diagnosis of a shock-related state in a patient bymeasure the capillary filling time and rate according to the secondembodiment of the invention. Device 500 includes a pulsating lightsource 501, such as a Light Emitting Diode (LED) driven by a rectangularvoltage pulse generator at a predetermined frequency fo. Light source501 is enclosed in a light-reflecting external housing 502 having anopening in its bottom side so that most of the light radiation emittedfrom light source 501 is directed toward the bottom side in onedirection “A”. External housing 502 has within it an opaque internalhousing 504 containing a light sensor 503, such as a photodiode, aphototransistor, a photo-resistor or a photoelectric cell. Internalhousing 504 has an opening in its bottom side which permits light raysto enter therein only through its bottom side. The bottom sides ofexternal housing 502 and internal housing 504 are aligned with eachother and are covered by a transparent rigid layer 505. This layerserves to apply pressure on the skin while enabling light to passtherethrough in both directions.

Transparent rigid layer 505 of device 500 is pressed into contact withthe exterior layer 506 of the skin. Pressure is applied manually orautomatically on the external housing 502 toward the skin surface in aperpendicular direction. The external housing delivers the pressure tothe transparent rigid layer 505 which transfers it through exteriorlayer 506 to the interior layer 507 of the skin containing most of thesubcutaneous blood vessels (capillaries).

As a result, when the magnitude of the applied pressure is adequate andis maintained for sufficient period of time, blood is then forced out ofthe pressurized capillaries and the color of the interior layer 507 ofskin becomes much brighter (i.e. substantially white). Light raysemitted from light source 501 penetrate into the skin and are partiallyreflected back in direction “B”, into the internal housing 504. Thedegree of reflection from interior layer 507 is inversely related toblood flow in the capillaries under pressure inasmuch as blood absorbslight the more blood in the capillaries the lesser is the reflectedlight.

The reflected light is aggregated by light sensor 503 which yields anelectric signal whose magnitude depends on the instantaneous color ofthe skin. Under zero pressure (i.e., full blood flow), the skin color isnormally pink and therefore less light is reflected back from thecapillaries. When the skin is subjected to pressure and blood isexpelled from the capillaries, the skin color is then white. Hence whenthe skin is pink, the intensity of reflected light is relatively low andwhen the skin is white the intensity of reflected light is significantlyhigher. As a consequence, changes in magnitude of the electric signalproduced by light sensor 503 affords an accurate measure of thecapillary filling time and rate. The Device 500 is connected to a pulsedpower supply for energizing light source 501 and for operating datacollection, processing and display circuitry to process the signalsyielded by light sensor 503 and for displaying the measurement results.

FIG. 6 is a block diagram of an apparatus 600 in the second embodimentfor diagnosing a shock-related state in a patient by measuring capillaryfilling time and rate. Apparatus 500 comprises a rectangular pulseoscillator 601 operated at a frequency fo=18 KHz. The output ofoscillator 601 is fed into a driver 602 which provides rectangularoutput pulses having sufficient energy to power light source 601 ′ toemit light pulses at the same frequency fo. Light reflected from theskin is converted by light sensor 603 to a corresponding pulsatoryelectrical signal. The signal is fed into an amplifier 604 operatingwithin a frequency band that includes frequency fo to increase theamplitude of the electrical signal.

Light sensor 603 is most sensitive to light radiation between red andinfra-red in the color spectrum but also to background light sources,such as external light radiation which adds an unwanted 50/60 Hz signal,or to sunlight which adds an unwanted DC level. Therefore the electricaloutput signal includes interfering components as well as the desiredcomponent at frequency fo. The interfering components are reduced inmagnitude by the amplifier 604 which is tuned to amplify the desiredcomponent at frequency fo to a greater degree than the unwantedcomponents.

The amplified electrical signal from amplifier 604 is further filteredby a Band-Pass-Filter (BPF) 605. This filter is tuned to pass only thedesired component at frequency fo and to reject all other unwantedcomponents. BPF 605 is implemented as an active filter using IntegratedCircuit (IC) technology. The resultant filtered signal at the output ofBPF 605 is a rectified sine wave which is fed into an integrator circuit606. Integrated Circuit 606 outputs a Direct Current (DC) levelproportional to the magnitude of the rectified sine wave and hence themagnitude of light reflected from the skin. It is therefore highlysensitive to changes in skin color.

The DC signal is fed into an Analog to Digital Converter (ADC) 607,which converts the DC level into a corresponding digital word. Thedigital data is fed into a digital processor 608 which analyzes the dataand display the results on a suitable display 609. Display 609 exhibitsa digital value representing the measurement results (i.e., the CFT),and a graphical representation of the measurement process as a functionof time. The graphical representation provides an indication of whetheror not the measurement results are reasonable, and if desired, themeasurement can be repeated. Other data processed results, such asstatistical data, can be also displayed to provide indications relatedto the reaction of the patient to medical treatment.

FIG. 3A which is a graphical representation of the measurement resultsof the CFT obtained with the first embodiment of the invention is alsorepresentative of the results obtained with the second embodiment. Atthe first stage, no pressure is applied on the skin and therefore thediagnostic apparatus can carry out calibration of the initial skin colorof the patient which is a shade of pink.

The calibration value is stored for use at the conclusion of themeasurement. The calibration process is essential, since the normalcolor of the skin depends on the individual being tested and differssomewhat from patient to patient. At the second stage, pressure isapplied with a magnitude and duration sufficient to obtain maximumwhitening of the skin color in the depressed area. The processor can beprogrammed to provide a warning signal (such as a beep) to the user,that the pressure is not sufficient or is shorter in duration thanrequired. Obtaining maximum whitening of the entire depressed area isindicative of sufficient pressure.

After obtaining maximum whitening, a corresponding signal is providedinstructing the user to quickly release the pressure. Measurement of theCFT is initialed at that moment, “to”. The skin coloring proceeds tochange from maximum whitening to essentially the original pinkish color.Normally, the rate of filling is higher at the beginning of the fillingprocess and lower as time lapses. The apparatus uses the storedcalibration value to determine the moment tf, at which the original skincolor is recovered and the measurement terminated. Recovery time can bedetermined in accordance with the desired measurement accuracy. Forexample, tf can be defined as the instant at which the value of thedigital word that corresponds to the current skin color reaches a valuewhich is 90% of the value of the digital word that corresponds to theoriginal skin color of the patient being tested. In the graph of FIG.3A, the CFT is given by tf-to.

The accuracy of the measurement can also be determined by the rate ofchange in the skin coloring, in the time interval that is close to thecompletion of the measurement. The last segment of the graph appearsbetween the time points t1 and tf. The rate of change in this timeinterval is nearly constant, and is almost insensitive to the magnitudeand duration of the applied pressure. Hence the CFT can be extrapolatedwith relative accuracy from the the interval tf-t1.

The CFT under normal shock-free conditions should be below 1 Sec. When aCFT value rising above 2 Sec is diagnosed. This is indicative of apre-shock state. Longer CFT values indicate a more severe shockcondition.

FIG. 3B which is a graphical representation of the CFT in the firstembodiment for obtaining inferences related to the trend of thepatient's physiological condition in reaction to medical treatment, isalso applicable to the second embodiment.

Modified Second Embodiment: The color sensor included in the secondembodiment of CFT diagnostic apparatus does not take into account thetemperature of the patient's skin at the time of the diagnosis and itseffect on the CFT reading. For accurate readings it is necessary tomeasure the skin surface temperature and record it prior to each CFTmeasurement.

In order to factor into the processing of the reflected light intensitythe influence thereon of skin temperature, included in the color sensorshown in FIG. 6 is a heat sensor 610, such as an infrared detector or athermistor, whose output signal varies in magnitude as a function of theintensity of infrared rays emanating from the skin surface in the courseof CFT diagnosis. Infrared detector 610 is responsive only to the heatof the skin, not to light reflected from the skin surface.

The electrical signal yielded by heat sensor 610 is not pulsed and has amagnitude which is a function of skin temperature. This signal isdigitized in an A/D converter 611 whose digital output is entered intocomputer microprocessor 608. Microprocessor 608 is programmed bysoftware to factor into the CFT reading the effect thereon of skintemperature. This corrected reading is of value in real time diagnosisof a patient's shock-related state, for it takes into account the skintemperature of the patient when in shock. It is of somewhat lesser valuewhen monitoring the condition of a patient being treated for shock.

A preferred form of skin temperature sensor is a thermometer which canbe placed directly on the skin surface of a patient being diagnosed forshock, to provide an electrical signal whose magnitude depends on theexisting skin temperature. The thermometer signal is entered intomicroprocessor 608 of a computer into which is also entered the CFTsignal indicative in terms of seconds, the shock state of the patient.

FIG. 8 illustrates the effect of skin temperature on CFT readings forpatients 1 and 2 having different skin temperatures T1 and T2. It willbe seen that in a normal no-shock state, the CFT readings which indicatethis state in terms of seconds are different, thereby reflecting theeffect on the CFT readings of the degree of difference betweentemperatures T1 and T2. Similar differences appear for the pre-shock andshock states.

A CFT instrument in accordance with the invention is a non-invasivediagnostic tool which determines the degree to which a patient is in astate of shock, making it possible for a clinician to prescribe atreatment that may save the patient's life. This instrument affords thefield of medicine with a new vital sign.

Existing vital signs (pulse rate, respiratory rate, body temperate andoften blood pressure) are important signs of life. Also highlysignificant is a patient's CFT, for this indicates whether a patient isin shock and is in danger of losing his life.

While there has been shown preferred embodiments of CFT instrumentation,it is to be understood that many changes may be made therein withoutdeparting from the spirit of the invention.

What is claimed is:
 1. A diagnostic medical instrument adapted todetermine whether a patient is suffering from a pre-shock, shock orshock-related condition, the instrument being used in a capillaryfilling time (CFT) test procedure in which a skin area of the patientoverlying blood-filled capillaries normally imparting to the skin a pinkcolor is depressed by a pressure which is sufficient to expel blood fromthe capillaries while maintaining normal flow in the veins, saidpressure causing the skin to blanch until the skin exhibits a whitecolor, the said pressure being released when a point of maximumblanching is reached to permit blood to flow back to the capillaries ata rate that depends on the condition of the patient to cause the skin toregain its natural pink color; said instrument comprising: i) meansincluding a color sensor trained on the skin area when exposed to lightto generate a signal having a magnitude which is a function of lightreflected by the skin area whose intensity depends on the natural colorof the skin area; ii) means responsive to said signal before pressure isapplied to the skin area to determine its natural pink color toestablish a reference base for the test to follow; and iii meansresponsive to said signal when pressure is applied to said skin duringthe test to measure the time elapsing from a starting point in time whenthe depressed skin is at its maximum blanching value of white, and thepressure applied thereon is then released to cause the capillaries toproceed to fill with blood, to a final point in time when the skinrecovers its natural pink color as established by the reference base,whereby the CFT measurement is an index to whether the patient issuffering from a shock-related condition, and to the severity of thiscondition.
 2. An instrument as set forth in claim 1, further including atemperature sensor responsive to heat radiating from the skin area togenerate a temperature signal that reflects the existing temperature ofthe skin area, and means to factor into the CFT measurement thetemperature signal to compensate the CFT measurement for the effect ofskin temperature thereon.
 3. An instrument as in claim 2, in which thetemperature sensor is a thermometer placed on the skin area to produce asignal whose magnitude depends on the existing skin temperature.
 4. Aninstrument as in claim 1, wherein the color sensor means includes avideo camera responsive to light reflected from the skin area to yieldan image signal whose character depends on an existing skin color.
 5. Anapparatus as in claim 1, in which the color sensor means includes meansto illuminate the skin area with modulated light from a light source,and a pulsed light reflected therefrom is intercepted by a photodetectorwhich yields a signal that depends on an existing skin color.
 6. Aninstrument as set forth in claim 1, further including means to applypressure to said skin area and means to control the magnitude and/orduration of the pressure so as to apply to the skin area the minimumamount of pressure necessary to cause the skin to exhibit a white color.7. A method for the diagnosis of a shock-related state in a patient bymeasuring the filling time of blood vessels subjacent to skin area ofthe patient, comprising the steps of: illuminating the area which is tobe gauged for color with a modulated light from a light source,filtering out background noises to obtain a base-line measurement, anddetermining the filling time of blood vessels in said area by comparisonof a current color of the area with the base-line measurement.
 8. Amethod according to claim 7, comprising: i) illuminating the area havingan original color with modulated light from a light source; ii)intercepting light reflected from the area with a light sensor, saidlight sensor producing a first signal having a magnitude whichcorresponds to the color of said area, said color representing the levelof reflection; iii) filtering said first signal for rejecting unwantedsignals derived from interfering light, and producing a second signalwhose amplitude is proportional to the amplitude of said filtered firstsignal; iv) storing the amplitude value of said second signal whichcorresponds to said original color; v) applying a pressure on said area,the magnitude of said pressure and its duration is sufficient to expelblood from said blood vessels to blanch the skin, up to maximumblanching and whitening of said area; and vi) measuring the filling timeof blood vessels by rapidly releasing said pressure and subsequentlymeasuring the amplitude of the second signal and displaying the totalperiod of time from maximum whitening at the time of pressure releaseuntil the amplitude of said second electrical signal is essentiallysimilar to said stored amplitude value, said total period of time beingindicative of a shock-related state in said patient and its severity. 9.A method according to claim 8, further comprising: i) sampling theamplitude value of the second electrical signal at a predetermined rateduring said measurement and storing said sampled values; and ii)extrapolating the capillary filling time by processing at least aportion of said stored values whenever the rate of change of thecapillary filling time remains substantially insensitive to themagnitude and/or duration of the applied pressure.
 10. A methodaccording to claim 9, wherein an alert signal is provided whenever thestrength and/or duration of the applied pressure be insufficient forobtaining maximum whitening.
 11. A method according to claim 8, whereinthe pressure is applied and released automatically.
 12. A methodaccording to claim 8, further including the step of verification of themeasurement by displaying a graphical representation of the measuredcapillary filing time.
 13. A method according to claim 8, furtherincluding the steps of: i) repeating the measurement of the capillaryfilling time at different time intervals; ii) storing the values of allmeasurements; and iii) displaying a graphical representation of themeasured filling times as a function of time, thereby obtaining aderivative of the capillary filling time on time d[CFT]/d[t], saidderivative being an indication related to the recovery or deteriorationof the patient from an actual or pre-shock state.
 14. A method accordingto claim 8, wherein the light is emitted from a LED.
 15. A methodaccording to claim 8, wherein the light is modulated by rectangularpulses at a predetermined rate.
 16. A method according to claim 8,wherein the light sensor is a photodetector selected from the groupconsisting of a photo-diode, a photo-transistor, a photo-resistor and aphotoelectric cell.
 17. A method according to claim 8, wherein thesecond electrical signal is produced by integrating the absolute valueof the filtered signal.
 18. A method according to claim 8, whereinpressure is applied by means of a rigid transducer containing a lightsource and a light sensor, said transducer being provided with atransparent wall that engages an appendage of the patient, a controlledforce being imposed on said rigid transducer toward the surface of saidappendage.
 19. A method according to claim 18, wherein the appliedpressure is controlled by means of a motor arranged to apply a force onsaid transducer.
 20. A method according to claim 18, wherein the appliedpressure is controlled by means of an electromagnet applying a force onsaid transducer.
 21. A method according to claim 7, wherein the bloodvessels are capillaries.
 22. Apparatus for the diagnosis of ashock-related state in a patient and of recovery of a patient therefromcomprising: i) means for illuminating a skin area of the patient to begauged for color with a light from a light source; ii) means formodulating said light; iii) means for filtering out background noisesand light to obtain a base-line measurement; and iv) means for comparingthe color of the skin area with the base-line measurement, therebydetermining the filling time of blood vessels in said area. 23.Apparatus for the diagnosis of a shock-related state in a patient and ofrecovery of a patient therefrom, comprising: i) a light source forilluminating an area of the patient's skin overlying blood vessels, saidarea having an original color; ii) means for modulating light emittedfrom said light source at a predetermined frequency; iii) a light sensorfor intercepting light reflected from said area and producing a firstsignal having a magnitude which corresponds to the color of said area,said color representing the level of reflection from blood vesselssubjacent said area; iv) a filter for filtering said first electricalsignal and for rejecting unwanted electrical signals originating ininterfering light, and for producing a second signal, whose amplitude isproportional to the amplitude of said filtered first signal; v) meansfor storing the amplitude value of said second signal which correspondsto said original color; vi) a transducer for applying pressure on saidarea, and for obtaining an amplitude of the second signal whichcorresponds to maximum whitening of said area; vii) a processor forprocessing data collected by said transducer and for measuring thefilling time of blood vessels after releasing said pressure; and viii)means for graphically displaying aid processed data.
 24. Apparatusaccording to claim 23, further including means for sampling theamplitude value of the second electrical signal at a predetermined rateduring the measurement and for storing said sampled values. 25.Apparatus according to claim 24, further comprising means forautomatically applying and releasing said pressure.
 26. A method for thediagnosis of physiological distress in a patient and for recovery of apatient from a state of physiological distress by measuring the fillingtime of blood vessels underlying an area of the skin of said patient,comprising the steps of: acquiring an image of skin area to be gaugedfor color to obtain a base-line color measurement, and determining thefilling time of blood vessels in said area by comparison of the color ofat least one more additional images of the gauged skin area with saidbase-line color measurement.
 27. A method according to claim 26,comprising the steps of: i) positioning image acquisition means so thatan area of the skin lies substantially within the focal plane thereof;ii) illuminating said area having an original color with light radiationat a level enabling said image acquisition means to discriminate betweencolors; iii) acquiring an image of said area with said image acquisitionmeans; iv) deriving a signal from said image, said signal representativeof the color of the said area; v) storing the value of said signal whichcorresponding to said original color; vi) applying pressure on saidarea, said pressure having a magnitude and duration sufficient to expelblood out from said blood vessels, and for obtaining a signal having avalue which corresponds to the maximum whitening of said area; vii)measuring the filling time by rapidly releasing said pressure andsubsequently measuring and displaying the total period of time frommaximum whitening until the value of said signal is substantially thesame as said stored value; and viii) determining the physiologicaldistress from said total period of time.
 28. A method according to claim27, wherein the illumination is obtained from background light.
 29. Amethod according to claim 27, wherein the illumination is obtained froma light source.
 30. A method according to claim 27, further includingthe step of verification of the measurement by displaying a graphicalrepresentation of the measured filling rate.
 31. A method according toclaim 27, further comprising: i) repeating the measurement of thefilling time at different time intervals; ii) storing the values of allmeasurements; and iii) displaying a graphical representation of themeasured filling times as a function of time, thereby obtaining aderivative of the capillary filling time on time d[CFT]/d[t], saidderivative being an indication related to deterioration in the patient'sphysiological condition, or to the recovery of the patient fromphysiological distress.
 32. A method according to claim 27, wherein theblood vessels are capillaries.
 33. Apparatus for the diagnosis ofphysiological distress in a patient and of recovery of a patient fromphysiological distress in accordance with changes in color of thepatient's skin in response to an applied pressure on said skin, saidpressure expelling blood from blood vessels subjacent to said skin, saidapparatus comprising: i) image acquisition means for acquiring an imageof an area of the skin of said patient to be gauged for color, saidimage acquisition means being trained in the area so that it liesessentially within the focal plane of said image acquisition means; ii)means for obtaining a base-line color measurement using the acquiredimage data corresponding to the color of said area when essentially nopressure is applied thereto; and iii) means for comparing the color ofsaid area with the base-line color measurement, thereby determining thefilling time of blood vessels in said area after releasing saidpressure.
 34. Apparatus according to claim 33, further comprising meansfor illuminating the area of the skin to be gauged for coloring withlight radiation at a level sufficient to enable the image acquisitionmeans to discriminate between colors.
 35. Apparatus according to claim34, wherein the image acquisition means is a video camera.
 36. Apparatusaccording to claim 34, further comprising a transducer for applyingpressure on said area, and for obtaining a signal value, whichcorresponds to maximum whitening of said area.